The Cytoplasmic yeast pyruvate decarboxylase under investigation is isolated from active dry baker's yeast strain 1821 obtained from Standard Brands. The enzyme is an oligomer which dissociates into subunits of one half the original molecular weight over pH 8.0. Additional investigation of the subunit composition of this enzyme can be summed as follows: 1) It has not been possible to demonstrate smaller units in the presence of urea with sephadex G-200. 2) Data obtained via the sodium dodecyl sulfate disc electrophoresis technique of Weber et al indicate that the protein is a tetramer and the molecular weight of the monomer unit is 60,000 plus or minus 2,700 daltons. The identity or nonidentity of the monomer units is currently under investigation. In order to minimize the effects of possible contaminating proteolytic enzymes during isolation, the preparative procedure has been modified to include incubation of cell extract with the proteolytic inhibitors, phenyl methyl sulfonyl fluoride and di-isopropyl fluorophosphate. Experimental investigations of the active site with bromopyruvate, a substrate analogue are in progress.